Process for preparing indoles

ABSTRACT

An indole of the formula ##STR1## can be prepared by subjecting an aniline of the formula: ##STR2## and a glycol or an oxide of the formula: ##STR3## to vapor phase reaction at 250° to 400° C. in the presence of a solid acid catalyst having dehydrating and dehydrogenating activities. 
     (In the above-mentioned formulae, R 1  stands for hydrogen, alkyl, aryl or aralkyl, R 2  stands for alkyl or alkoxy, R 3  and R 4  are the same or different and stands for hydrogen or alkyl, R 5  and R 6  are the same or different and stand for hydrogen or alkyl, and n is an integer of 0 to 4.)

TECHNICAL FIELD

This invention relates to a process for preparing indoles. More particularly, it relates to a process for preparing indoles by a vapor phase reaction of anilines with glycols or oxides in the presence of a solid acid catalyst having dehydrating and dehydrogenating activities.

TECHNICAL BACKGROUND

Indoles are useful as starting materials for tryptophan, aromatics, medicines, agricaltural chemicals, stabilizers for polymers, and the like. Various methods have been known for preparation of indoles by a vapor phase reaction. For example, Japanese Patent Publication (unexamined) No. 78163/1973 discloses that indoles are prepared by contacting 2-alkylanilines at 500° to 750° C. with an iron oxide catalyst containing an alkali metal compound. Japanese Patent Publication (unexamined) No. 57966/1973 discloses that indoles are prepared by contacting o-nitroalkylbenzene at 300° to 550° C. with a catalyst containing ruthenium, palladium or platinum. Further, Japanese Patent Publication (unexamined) No. 65266/1977 discloses that indoles are prepared by contacting phenylhydrozines and a carbonyl compound at 300° C. with a Lewis acid (e.g., zinic chloride). Furthermore, Chemical Abstracts, Vol. 62 (1965), 16174h discloses that indole are prepared by contacting aniline and ethanol with an alumina catalyst or an iron oxide-alumina catalyst. Additionally, Chemical Abstracts, Vol. 63 (1965), 11477 g discloses that indole are prepared by contacting aniline and acetylene at 620° to 700° C. with an iron oxide-alumina catalyst. However, the methods described in Japanese Patent Publication (unexamined) No. 78163/1973 and Chemical Abstracts, Vol. 63 (1965), 11477 g are disadvantageous in that the vapor phase reaction must be carried out at a temperature higher than 500° C. In the method described in Japanese Patent Publication (unexamined) No. 57966/1973 it is necessary to use an expensive noble metal catalyst, and the methods described in Japanese Patent Publication (unexamined) Nos. 57966/1973 and 65266/1977 require the use of expensive o-nitro-alkylbenzene or phenylhydrazines as the starting material. Further, the methods described in Japanese Patent Publication (unexamined) Nos. 78163/1973 and 57966/1973, Chemical Abstracts, Vol. 62 (1965), 16174h an ibid. Vol. 63 (1965), 11477 g are disadvantageous in that N-substituted indoles can not be prepared directly.

OBJECTS OF THE INVENTION

An object of the present invention is to provide a method for preparing various indoles including N-substituted indoles from anilines and glycols (or oxides) both of which are less expensive and readily available in the market. Another object of the invention is to provide a method for preparing indoles by carrying out a vapor phase reaction at such a relatively low temperature as 250° to 400° C. Other object of the invention is to provide a method for preparing indoles advantageously in an industrial scale by using a conventional solid acid catalyst instead of such an expensive catlyst as the noble metal catalyst. These and further objects of the invention will become apparent from the following description.

DISCLOSURE OF THE INVENTION

As a result of various inventigations, we have now found that indoles can be readily prepared by reacting anilines with glycols or oxides in the vapor phase in the presence of a solid acid catalyst having dehydrating and dehydrogenating activities. Namely, according to the present invention, an indole of the formula: ##STR4## wherein R¹ stands for hydrogen, alkyl, aryl or aralkyl, R² stands for alkyl or alkoxy, R³ and R⁴ are the same or different and stand for hydrogen or alkyl, and n stands for an integer of 0 to 4, can be prepared by reacting an aniline of the formula: ##STR5## wherein R¹, R² and n are the same as defined above, with either a glycol of the formula: ##STR6## wherein R³ and R⁴ are the same as defined above, and R⁵ and R⁶ are the same or different and stand for hydrogen or alkyl, or an oxide of the formula: ##STR7## wherein R³ and R⁴ are the same as defined above, at a temperature of 250° to 400° C. in the vapor phase in the presence of a solid acid catalyst having dehydrating and dehydrogenating activities.

Preferred examples of the aniline to be used in the method of the present invention include those of the formula (I) in which R¹ is hydrogen; C₁₋₄ alkyl such as methyl, ethyl, n-propyl, isopropyl or n-butyl; aryl such as phenyl or substituted phenyl (e.g., phenyl substituted with C₁₋₄ alkyl or C₁₋₄ alkoxy such as methylphenyl or methoxyphenyl); or aralkyl such as benzyl or substituted benzyl (e.g., benzyl substituted with C₁₋₄ alkyl or C₁₋₄ alkoxy such as methylbenzyl or methoxybenzyl), R² is C₁₋₄ alkyl such as methyl, ethyl, n-propyl, isopropyl or n-butyl; or C₁₋₄ alkyoxy such as methoxy, ethoxy, n-propoxy or n-butoxy, and n is an integer of 0 to 4. Representative examples of such aniline include aniline, N-alkylaniline (e.g., N-methylaniline, N-ethylaniline), N-phenylaniline, N-benzylaniline, toluidine (e.g., o-toluidine, m-toluidine, p-toluidine), N-alkyltoluidine (e.g., N-methyl-o-toluidine, N-ethyl-o-toluidine, N-methyl-m-toluidine, N-ethyl-m-toluidine, N-methyl-p-toluidine, N-ethyl-p-toluidine), N-phenyltoluidine (e.g., N-phenyl-o-toluidine, N-phenyl-m-toluidine, N-phenyl-p-toluidine), N-benzyltoluidine (e.g., N-benzyl-o-toluidine, N-benzyl-m-toluidine, N-benzyl-p-toluidine), anisidine (e.g., o-anisidine, m-anisidine, p-anisidine), N-alkylanisidine (e.g., N-methyl-p-anisidine, N-ethyl-p-anisidine), N-phenylanisidine (e.g., N-phenyl-p-anisidine) and N-benzylanisidine (e.g., N-benzyl-p-anisidine).

On the other hand, preferred examples of the glycol include those of the formula (II) in which R³ and R⁴ are the same or different and are hydrogen or C₁₋₄ alkyl such as methyl, ethyl, n-propyl or n-butyl, and R⁵ and R⁶ are the same or different and are hydrogen or C₁₋₄ alkyl such as methyl, ethyl, n-propyl or n-butyl. Representative examples of such glycol include ethylene glycol, propylene glycol, 1,2-butylene glycol, 2,3-butylene glycol, ethylene glycol monoethyl ether and ethylene glycol mono-n-butyl ether.

Further, preferred examples of the oxide include those of the formula (II') in which R³ and R⁴ are the same or different and are hydrogen or C₁₋₄ alkyl such as methyl, ethyl, n-propyl or n-butyl. Representative examples of such oxide include ethylene oxide, 1,2-butylene oxide and 2,3-butylene oxide.

Any solid acid catalysts which have both dehydrating and dehydrogenating activities can be employed as the catalyst in the method of the present invention. Such catalyst includes, for example, a solid acid catalyst containing as its component at least one member selected from aluminum oxide, silicon dioxide and activated charcoal. Representative examples of such catalyst include silica catalyst, alumina catalyst, silica-alumina catalyst, pumice catalyst and activated charcoal catalyst. These catalysts may optionally contain a metal oxide. Examples of the metal oxide include an alkali metal oxide (e.g., sodium oxide, potassium oxide), an alkaline earth metal oxide (e.g., magnesium oxide, calcium oxide), zinc oxide, antimony oxide, bismuth oxide, vanadium oxide, chromium oxide, molybdenum oxide, thungsten oxide, iron oxide, nickel oxide, cobalt oxide, uranium oxide and thorium oxide. It is preferred that the catalyst contains the metal oxide in an amount not more than 50% by weight. Concomitantly, zeolite, either natural or synthetic, is included within the scope of the catalysts of the present invention because it is a kind of the silica-alumina catalysts.

Among the above-mentioned catalysts, a preferred subgenus includes silica catalyst, alumina catalyst, silica-alumina catalyst and these catalysts containing a metal oxide such as sodium oxide, potassium oxide, zinc oxide, chrominum oxide, iron oxide or nickel oxide.

The reaction of the present invention can be carried out by contacting the aniline (I) and the glycol (II) or the oxide (II') with the above-mentioned catalyst at 250° to 400° C. in the vapor phase.

In carrying out the reaction, it is preferred to vaporize the aniline (I) and the glycol (II) or the oxide (II') in a vaporizor and then introduce the vapor of said compounds into a reactor. In this case, preferred molar ratio of the glycol (II) or the oxide (II') to the aniline (I) is 0.5-10:1. Decomposition of the aniline may increase if said molar ratio is less than 0.5:1. On the other hand, side reactions may increase if the molar ratio is more than 10:1. These starting compounds should preferably be introduced into the reactor together with an inert diluent. Such inert diluent includes, for example, steam (water vapor), nitrogen gas, carbon dioxide gas, gaseous benzene, gaseous toluene or a mixture thereof. When such diluent is used, the initial partial pressure of the aniline (I) should be preferably within the range of 0.01 to 0.1 atm. It is preferred to carry out the reaction at 250° to 400° C., especially at 275° to 350° C. The reaction can be carried out either under reduced pressure, under atmospheric pressure or under increased pressure, but it is generally preferred to carry it out under atmospheric pressure. Further, a contact time (W/F) which is defined by the following formula should preferably be within the range of 10 to 1000 g-cat·hr/mole, especially 20 to 200g-cat.hr/mole ##EQU1##

The reaction mixture is cooled and collected as a condensed solution. While the resultant indoles and unreacted starting compounds are contained in the condensed solution, they are separated from each other by such a method as extraction or distillation or by converting them to acid addition salts thereof (e.g., hydrochloride). The starting compounds which remain unreacted can be reused for the reaction of the present invention.

The indoles prepared by the above-mentioned method of the present invention include, for example, indole, 1-methylindole, 1-ethylindole, 1-phenylindole, 1-benzylindole, 3-methylindole, 4-methylindole, 5-methylindole, 6-methylindole, 7-methylindole, 1,2-dimethylindole, 1,3-dimethylindole, 1,4-dimethylindole, 1,5-dimethylindole, 1,6-dimethylindole, 1,7-dimethylindole, 3,4-dimethylindole, 3,5-dimethylindole, 3,6-dimethylindole, 3,7-dimethylindole, 1-ethyl-2-methylindole, 1-ethyl-3-methylindole, 1-ethyl-4-methylindole, 1-ethyl-5-methylindole, 1-ethyl-6-methylindole, 1-ethyl-7-methylindole, 1,3-diethylindole, 1,3,7-trimethylindole, 1,3,4-trimethylindole, 1,3,5-trimethylindole, 1,3,6-trimethylindole, 1,2,5-trimethylindole, 1-ethyl-2,5-dimethylindole, 1-ethyl-3,5-dimethylindole, 1-ethyl-3,6-dimethylindole, 1-ethyl-3,7-dimethylindole, 1-benzyl-3-methylindole, 1-methyl-5-methoxyindole, 1,3-dimethyl-5-methoxyindole, 1-benzyl-5-methoxyindole and the like. Concomitantly, two kinds of indoles may be obtained depending on the starting compounds used. For example, 1,3-dimethylindole and 1,2-dimethylindole are obtained by using N-methylaniline and propylene glycol (or propylene (oxide) as the starting compounds. On the other hand, 4-methylindole and 6-methylindole are obtained by using m-toluidine and ethylene glycol as the starting compounds.

The above-mentioned method of the present invention is advantageous in that (I) indoles can be readily obtained from anilines and glycols (or oxides) which are less expensive and readily available in the market; (2) the vapor phase reaction can be carried out at a relatively low temperature (250° to 400° C.); (3) conventional solid acid catalysts can be used as the catalyst, and therefore it is not necessary to use a catalyst containing an expensive noble metal or a poisonous heavy metal; (4) various indoles can be prepared by suitably selecting the starting compounds; and (5) N-substituted indoles can be prepared in a high yield and in a high selectivity. Therefore, the method of the present invention is excellent for preparation of indoles.

The method of the present invention is explained by means of the following Examples, but these Examples should not be construed to limit the scope of the present invention. Throughout Examples, the analytical values were estimated by gas chromatography, and each product was identified by mass spectrum, nuclear magnetic resonance spectrum and infrared adsorption spectrum. Further, the conversion ratio of anilines, selectivity to indoles and yield of indoles are defined as follows: ##EQU2##

EXAMPLE 1

20 g of "Neobead P" (manufactured by Mizusawa Chemical Industry Co., Ltd.; Chemical compositions (% by weight), Al₂ O₃ : SiO₂ : Na₂ O=88:9:3) we packed into a tubular quartz-reactor of 22 mm in diameter and 300 mm in length, and heated in a tubular electric furnace. A mixed gas containing an aniline vapor, ethylene glycol vapor, water vapor, nitrogen gas and/or benzene vapor was introduced into the reactor under the following conditions.

    ______________________________________                                         Contact time (W/F): 49.6 g-cat · hr/mole                              Initial partial pressure (atm):                                                ______________________________________                                         Reaction Conditions A                                                          Anilines vapor    0.0205                                                       Ethylene glycol vapor                                                                            0.0409                                                       Water vapor       0.778                                                        Nitrogen gas      0.161                                                        Reaction Conditions B                                                          Anilines vapor    0.0227                                                       Ethylene glycol vapor                                                                            0.0454                                                       Water vapor       0.771                                                        Nitrogen gas      0.161                                                        Reaction Conditions C                                                          Anilines vapor    0.0205                                                       Ethylene glycol vapor                                                                            0.0409                                                       Water vapor       0.659                                                        Benzene vapor     0.119                                                        Nitrogen gas      0.161                                                        Reaction Conditions D                                                          Anilines vapor    0.0205                                                       Ethylene glycol vapor                                                                            0.0820                                                       Water vapor       0.619                                                        Benzene vapor     0.119                                                        Nitrogen gas      0.161                                                        ______________________________________                                    

The effluent gas was cooled by a condenser and collected as a condensed solution. The condensed solution was analyzed by gas chromatography about 3 hours after the reaction was started. The results are shown in the following Table 1.

                                      TABLE 1                                      __________________________________________________________________________                                          Selectivity                                               Reaction       Conversion                                                                           to main                                                                               Yield of main                                Reaction                                                                             temperature                                                                           Main indoles                                                                           of anilines                                                                          indoles                                                                               indoles produced                   No.                                                                               Anilines                                                                              conditions                                                                           (°C.)                                                                          produced                                                                               (%)   produced (%)                                                                          (%)                                __________________________________________________________________________     1  Aniline                                                                               A     350    Indole  54.0  23.6   12.8                               2  N--Methyl-                                                                            A     325    1-Methylindole                                                                         84.6  55.7   47.1                                  aniline                                                                     3  N--Ethyl-                                                                             A     300    1-Ethylindole                                                                          58.7  71.9   42.2                                  aniline                                                                     4  Diphenyl-                                                                             C     300    1-Phenylindole                                                                         56.0  87.9   49.2                                  amine                                                                       5  N--Benzyl-                                                                            C     300    1-Benzylindole                                                                         82.8  49.4   40.9                                  aniline                                                                     6  o-Toluidine                                                                           A     325    7-Methylindole                                                                         63.9  30.8   19.7                               7  N--Methyl-                                                                            A     325    1,7-Dimethyl-                                                                          61.2  33.5   20.5                                  o-toluidine         indole                                                  8  N--Ethyl-                                                                             B     325    1-Ethyl-7-                                                                             52.3  43.9   23.0                                  o-toluidine         methylindole                                            9  m-Toluidine                                                                           A     350    4-Methylindole                                                                         69.6  34.2   23.8                                                      &                                                                              6-Methylindole                                          10 N--Methyl-                                                                            A     300    1,4-Dimethyl-                                                                          59.4  93.4   55.5                                  m-toluidine         indole &                                                                       1,6-Dimethyl-                                                                  indole                                                  11 N--Ethyl-                                                                             A     325    1-Ethyl-4-                                                                             75.9  76.0   57.7                                  m-toluidine         methylindole                                                                   &                                                                              1-Ethyl-6-                                                                     methylindole                                            12 p-Toluidine                                                                           C     325    5-Methylindole                                                                         69.0  25.7   17.7                               13 N--Methyl-                                                                            A     300    1,5-Dimethyl-                                                                          74.1  76.0   56.3                                  p-toluidine         indole                                                  14 N--Ethyl-                                                                             A     300    1-Ethyl-5-                                                                             72.7  57.9   42.1                                  p-toluidine         methylindole                                            15 N--Methyl-                                                                            C     300    1-Methyl-5-                                                                            72.7  52.0   37.8                                  p-anisidine         methoxyindole                                           16 N--Benzyl-                                                                            D     300    1-Benzyl-5-                                                                            70.1  64.3   45.1                                  p-anisidine         methoxyindole                                           __________________________________________________________________________

EXAMPLE 2

The reaction was carried out in the same manner as described in Example 1 except that ethylene oxide was used instead of ethylene glycol. The results are shown in the following Table 2.

    ______________________________________                                         Reaction conditions                                                            Contact time (W/F): 49.6 g-cat · hr/mole                              Initial partial pressure (atm):                                                ______________________________________                                         Anilines vapor    0.0205                                                       Ethylene oxide vapor                                                                             0.0409                                                       Water vapor       0.778                                                        Nitrogen gas      0.161                                                        ______________________________________                                    

                                      TABLE 2                                      __________________________________________________________________________                                Selectivity                                                                          Yield of                                                Reaction         to main                                                                              main                                                    tempera-                                                                            Main  Conversion                                                                           indoles                                                                              indoles                                                 ture indoles                                                                              of anilines                                                                          produced                                                                             produced                                      No.                                                                               Anilines                                                                              (°C.)                                                                        produced                                                                             (%)   (%)   (%)                                           __________________________________________________________________________     1  Aniline                                                                               350  Indole                                                                               51.3  26.3  13.5                                          2  N--Methyl-                                                                            325  1-Methyl-                                                                            73.4  54.6  40.1                                             aniline     indole                                                          3  N--Ethyl-                                                                             300  1-Ethyl-                                                                             47.4  58.4  27.7                                             aniline     indole                                                          __________________________________________________________________________

EXAMPLE 3

The reaction was carried out in the same manner as described in Example 1 except that propylene glycol was used instead of ethylene glycol. The results are shown in the following Table 3.

    ______________________________________                                         Contact time (W/F): 49.6 g-cat · hr/mole                              Initial partial pressure (atm):                                                ______________________________________                                         Reaction conditions A                                                          Anilines vapor     0.0205                                                      Propylene glycol   0.0409                                                      Water vapor        0.778                                                       Nitrogen gas       0.161                                                       Reaction conditions B                                                          Anilines vapor     0.0205                                                      Propylene glycol vapor                                                                            0.0409                                                      Water vapor        0.659                                                       Benzene vapor      0.119                                                       Nitrogen gas       0.161                                                       ______________________________________                                    

                                      TABLE 3                                      __________________________________________________________________________                                          Selectivity                                               Reaction       Conversion                                                                           to main                                                                               Yield of main                                Reaction                                                                             temperature                                                                           Main indoles                                                                           of anilines                                                                          indoles                                                                               indoles produced                   No.                                                                               Anilines                                                                              conditions                                                                           (°C.)                                                                          produced                                                                               (%)   produced (%)                                                                          (%)                                __________________________________________________________________________     1  Aniline                                                                               A     300    3-Methylindole                                                                         63.4  31.9   20.2                               2  N--Methyl-                                                                            A     300    1,3-Dimethyl- 46.1   23.2                                  aniline             indole                                                                         1,2-Dimethyl-                                                                          50.3  14.5   7.3                                                       indole                                                  3  N--Ethyl-                                                                             A     300    1-Ethyl-3-    45.8   21.4                                  aniline             methylindole                                                                   1-Ethyl-2-                                                                             46.7  13.7   6.4                                                       methylindole                                            4  N--Benzyl-                                                                            B     300    1-Benzyl-3-                                                                            49.5  71.0   35.1                                  aniline             methylindole                                            5  o-Toluidine                                                                           A     300    3,7-Dimethyl-                                                                          70.9  79.0   56.0                                                      indole                                                  6  N--Methyl-                                                                            A     300    1,3,7-Trimethyl-                                                                       39.4  31.9   12.6                                  o-toluidine         indole                                                  7  N--Ethyl-                                                                             A     300    1-Ethyl-3,7-                                                                           29.1  40.6   11.8                                  o-toluidine         dimethylindole                                          8  m-Toluidine                                                                           A     325    3,4-Dimethyl-                                                                          82.0  45.0   36.9                                                      indole &                                                                       3,6-Dimethyl-                                                                  indole                                                  9  N--Methyl-                                                                            A     275    1,3,4-Trimethyl-                                                                       55.8  47.3   26.4                                  m-toluidine         indole &                                                                       1,3,6-Trimethyl-                                                               indole                                                  10 N--Ethyl-                                                                             A     300    1-Ethyl-3,4-                                                                           50.6  30.8   15.6                                  m-toluidine         dimethylindole                                                                 &                                                                              1-Ethyl-3,6-                                                                   dimethylindole                                          11 p-Toluidine                                                                           B     300    3,5-Dimethyl-                                                                          76.2  31.5   24.0                                                      indole                                                  12 N--Methyl-                                                                            A     300    1,3,5-Trimethyl-                                                                             72.8   49.1                                  p-toluidine         indole                                                                         1,2,5-Trimethyl-                                                                       67.5  20.6   13.9                                                      indole                                                  13 N--Ethyl-                                                                             A     300    1-Ethyl-3,5-  73.7   37.0                                  p-toluidine         dimethylindole                                                                 1-Ethyl-2,5-                                                                           50.2  19.3   9.7                                                       dimethylindole                                          14 N--Methyl-                                                                            B     300    1,3-dimethyl-5-                                                                        67.4  44.4   29.9                                  p-anisidine         methoxyindole                                           __________________________________________________________________________

EXAMPLE 4

The reaction was carried out in the same manner as described in Example 1 except that propylene oxide was used instead of ethylene glycol. The results are shown in the following Table 4.

    ______________________________________                                          Reaction conditions                                                           Contact time (W/F): 49.6 g-cat · hr/mole                              Initial partial pressure (atm):                                                ______________________________________                                         Anilines vapor    0.0205                                                       Propylene oxide vapor                                                                            0.0409                                                       Water vapor       0.778                                                        Nitrogen gas      0.161                                                        ______________________________________                                    

                                      TABLE 4                                      __________________________________________________________________________                                Selectivity                                                                          Yield of                                                Reaction         to main                                                                              main                                                    tempera-                                                                            Main  Conversion                                                                           indoles                                                                              indoles                                                 ture indoles                                                                              of anilines                                                                          produced                                                                             produced                                      No.                                                                               Anilines                                                                              (°C.)                                                                        produced                                                                             (%)   (%)   (%)                                           __________________________________________________________________________     1  Aniline                                                                               350  3-Methyl-                                                                            55.7  21.5  12.0                                                         indole                                                          2  N--Methyl-                                                                            300  1,3-Di-     38.5  19.6                                             aniline     methyl-                                                                        indole                                                                         1,2-Di-                                                                              50.9  9.4   4.8                                                          methyl-                                                                        indole                                                          3  N--Ethyl-                                                                             300  1-Ethyl-    36.7  17.5                                             aniline     3-methyl-                                                                      indole                                                                         1-Ethyl-                                                                             47.7  8.0   3.8                                                          2-methyl-                                                                      indole                                                          __________________________________________________________________________

EXAMPLE 5

The reaction was carried out in the same manner as described in Example 1 except that ethylene glycol monomethyl ether was used instead of ethylene glycol. The results are shown in the following Table 5.

    ______________________________________                                         Reaction conditions                                                            ______________________________________                                         Contact time (W/F)   49.6 g-cat · hr/mole                             Initial partial pressure (atm)                                                 Anilines vapor       0.0205                                                    Ethylene glycol monomethyl                                                                          0.0409                                                    ether vapor                                                                    Water vapor          0.778                                                     Nitrogen gas         0.161                                                     ______________________________________                                    

                                      TABLE 5                                      __________________________________________________________________________                                Selectivity                                                                          Yield of                                                Reaction         to main                                                                              main                                                    tempera-                                                                            Main  Conversion                                                                           indoles                                                                              indoles                                                 ture indoles                                                                              of anilines                                                                          produced                                                                             produced                                      No.                                                                               Anilines                                                                              (°C.)                                                                        produced                                                                             (%)   (%)   (%)                                           __________________________________________________________________________     1  N--Methyl-                                                                            325  1-Methyl-                                                                            80.7  34.0  27.4                                             aniline     indole                                                          2  N--Ethyl-                                                                             325  1-Ethyl-                                                                             69.5  34.8  24.2                                             aniline     indole                                                          __________________________________________________________________________

EXAMPLE 6

The reaction was carried out in the same manner as described in Example 1 except that ethylene glycol mono-n-butyl ether was used instead of ethylene glycol. The results are shown in the following Table 6.

    ______________________________________                                         Reaction conditions                                                            ______________________________________                                         Contact time (W/F)   49.6 g-cat · hr/mole                             Initial partial pressure (atm)                                                 Anilines vapor       0.0205                                                    Ethylene glycol mono-n-buthyl                                                                       0.0409                                                    ether vapor                                                                    Water vapor          0.778                                                     Nitrogen gas         0.161                                                     ______________________________________                                    

                                      TABLE 6                                      __________________________________________________________________________                                Selectivity                                                                          Yield of                                                Reaction         to main                                                                              main                                                    tempera-                                                                            Main  Conversion                                                                           indoles                                                                              indoles                                                 ture indoles                                                                              of anilines                                                                          produced                                                                             produced                                      No.                                                                               Anilines                                                                              (°C.)                                                                        produced                                                                             (%)   (%)   (%)                                           __________________________________________________________________________     1  N--Methyl-                                                                            325  1-Methyl-                                                                            52.1  46.9  24.5                                             aniline     indole                                                          2  N--Ethyl-                                                                             325  1-Ethyl-                                                                             58.6  33.1  19.4                                             aniline     indole                                                          __________________________________________________________________________

EXAMPLE 7

The reaction was carried out in the same manner as described in Example 1 except that 1,2-buthylene glycol was used instead of ethylene glycol. The results are shown in the following Table 7.

    ______________________________________                                         Reaction conditions                                                            ______________________________________                                         Contact time (W/F)   49.6 g-cat · hr/mole                             Initial partial pressure (atm)                                                 Anilines vapor       0.0205                                                    1,2-Buthylene glycol vapor                                                                          0.0307                                                    Water vapor          0.788                                                     Nitrogen gas         0.161                                                     ______________________________________                                    

                                      TABLE 7                                      __________________________________________________________________________                               Selectivity                                                                          Yield of                                                Reaction         to main                                                                              main                                                    tempera-                                                                            Main  Conversion                                                                           indoles                                                                              indoles                                                 ture indoles                                                                              of anilines                                                                          produced                                                                             produced                                       No.                                                                               Anilines                                                                             (°C.)                                                                        produced                                                                             (%)   (%)   (%)                                            __________________________________________________________________________     1  N--Ethyl-                                                                            300  1,3-diethyl-                                                                         36.1  53.7  19.4                                              aniline    indole                                                           __________________________________________________________________________

EXAMPLE 8

30 g of a catalyst shown in Table 8 were packed into a tubular quartz-reactor (22 mm in diameter, 300 mm in length), and then heated by a tubular electric furnace. A mixed gas of aniline vapor, ethylene glycol vapor, water vapor and nitrogen gas was introduced into the reactor under the following conditions.

    ______________________________________                                         Reaction conditions                                                            ______________________________________                                         Contact time (W/F)   74.4 g-cat · hr/mole                             Initial partial pressure (atm)                                                 Aniline vapor        0.0205                                                    Ethylene glycol vapor                                                                               0.0819                                                    Water vapor          0.737                                                     Nitrogen gas         0.161                                                     ______________________________________                                    

The effluent gas was cooled by a condensor and collected as a condensed solution. The condensed solution was analyzed by gas chromatography about 3 hours after the reaction was started. The results are shown in the following Table 8.

The chemical compositions (% by weight) of "Neobead P, C or D" (manufactured by Mizusawa Chenmical Industry Co., Ltd.) used as the catalyst are as follows:

"Neobead P"; Al₂ O₃ :SiO₂ :Na₂ O=88:9:3

"Neobead C"; Al₂ O₃ =100

"Neobead D"; Al₂ O₃ :SiO₂ =90:10

                  TABLE 8                                                          ______________________________________                                                                           Select-                                                                               Yield                                                 Reaction  Conversion                                                                             ivity  of                                                    temper-   of aniline                                                                             to indole                                                                             indole                                No.  Catalysts  ature (°C.)                                                                       (%)     (%)    (%)                                   ______________________________________                                         1    Neobead P  300       82.3    15.4   12.7                                                  350       71.0    18.3   13.0                                  2    Fe.sub.2 O.sub.3 (10%)-                                                                   300       91.0    14.9   13.6                                       Neobead P  350       76.1    16.0   12.2                                  3    Fe.sub.2 O.sub.3 (10%)-                                                                   300       80.9    10.9   8.8                                        Neobead C  350       78.8    17.5   13.8                                  4    Fe.sub.2 O.sub.3 (10%)-                                                                   300       96.9    14.3   13.9                                       Neobead D  350       75.5    16.4   12.4                                  5    ZnO (10%)- 300       83.6    11.1   9.3                                        Neobead C  350       87.5    12.0   10.5                                  6    Cr.sub.2 O.sub.3 (10%)-                                                                   300       81.5    11.9   9.7                                        Neobead C  350       74.5    14.1   10.5                                  7    NiO (10%)- 350       74.2    21.1   15.7                                       Neobead C  400       41.4    23.7   9.8                                   ______________________________________                                    

EXAMPLE 9

The reaction of N-ethylaniline with ethylene glycol was carried out over a catalyst shown in Table 9 in the same manner as described in Example 1, whereby 1-ethylindole was obtained as a main product. The results are shown in the following Table 9.

    ______________________________________                                         Reaction conditions A                                                          Contact time (W/F)   49.6 g-cat · hr/mole                             Initial partial pressure (atm)                                                 N--Ethylaniline vapor                                                                               0.0205                                                    Ethylene glycol vapor                                                                               0.0409                                                    Water vapor          0.778                                                     Nitrogen gas         0.161                                                     Reaction conditions B                                                          Contact time (W/F)   24.8 g-cat · hr/mole                             Initial partial pressure (atm)                                                 N--Ethylaniline vapor                                                                               0.0205                                                    Ethylene glycol vapor                                                                               0.0409                                                    Water vapor          0.778                                                     Nitrogen gas         0.161                                                     ______________________________________                                    

                                      TABLE 9                                      __________________________________________________________________________                     Reaction                                                                            Conversion                                                                            Selectivity                                                                          Yield of                                                     tempera-                                                                            of N--ethyl-                                                                          to 1-ethyl-                                                                          1-ethyl-                                               Reaction                                                                             ture aniline                                                                               indole                                                                               indole                                       No.                                                                               Catalysts                                                                             conditions                                                                           (°C.)                                                                        (%)    (%)   (%)                                          __________________________________________________________________________     1  Neobead P                                                                             A     300  58.7   71.9  42.2                                         2  Neobead P                                                                             B     350  53.5   52.1  27.9                                         3  NiO (10%)-                                                                            B     350  38.5   56.1  21.6                                            Neobead P                                                                   4  Neobead D                                                                             A     250  56.9   22.3  12.7                                         5  Neobead C                                                                             A     250  46.5   19.8  9.2                                          6  K.sub.2 O (1%)-                                                                       A     300  75.8   35.2  26.7                                            Neobead C                                                                   7  K.sub.2 O (3%)-                                                                       A     300  56.0   45.5  25.5                                            Neobead C                                                                   8  K.sub.2 O (5%)-                                                                       A     300  37.6   73.9  27.8                                            Neobead C                                                                   9  K.sub.2 O (7%)-                                                                       A     350  50.6   62.8  31.8                                            Neobead C                                                                   10 K.sub.2 O (10%)-                                                                      A     350  33.8   47.6  16.1                                            Neobead C                                                                   __________________________________________________________________________

EXAMPLE 10

20 g of a catalyst shown in Table 10 were packed into a tubular quartz-reactor (22 mm in diameter, 300 mm in length), and then heated by a tubular electric furnace. A mixed gas of aniline vapor, ethylene oxide vapor, water vapor and nitrogen gas was introduced into the reactor under the following conditions.

    ______________________________________                                         Reaction conditions                                                            ______________________________________                                         Contact time (W/F)   49.6 g-cat · hr/mole                             Initial partial pressure (atm)                                                 Aniline vapor        0.0204                                                    Ethylene oxide vapor 0.0224                                                    Water vapor          0.796                                                     Nitrogen gas         0.161                                                     ______________________________________                                    

The effuent gas was cooled by a condensor and collected as a condensed solution. The condensed solution was analyzed by gas chromatography about 3 hours after the reaction was started. The results are shown in the following Table 10.

The chemical compositions (% by weight) of "Silica" (manufactured by Katayama Chemical Industry Co., Ltd.); SiO₂ =100

                  TABLE 10                                                         ______________________________________                                                                           Select-                                                                               Yield                                                Reaction  Conversion                                                                              ivity  of                                                   temper-   of aniline                                                                              to indole                                                                             indole                                No.  Catalysts ature (°C.)                                                                       (%)      (%)    (%)                                   ______________________________________                                         1    Neobead P 350       42.1     32.1   13.5                                  2    Silica    400       62.6     15.8   9.9                                   ______________________________________                                    

EXAMPLE 11

N-Ethylaniline and ethylene glycol were reacted at a molar ratio shown in Table 11 in the same manner as described in Example 1, whereby 1-ethylindole was obtained as a main product. The results are shown in the following Table 11.

    ______________________________________                                         Reaction conditions                                                            ______________________________________                                         Reaction temperature 300° C.                                            Contact time (W/F)   49.6 g-cat · hr/mole                             Initial partial pressure (atm)                                                 N--Ethyaniline vapor 0.0205                                                    Nitrogen gas         0.161                                                     Water vapor    (A) 0.808 (B) 0.798                                                            (C) 0.778 (D) 0.757                                             ______________________________________                                    

                                      TABLE 11                                     __________________________________________________________________________      No.                                                                               ##STR8##   conditionsReaction                                                                   (%)anilineof N--ethyl-Conversion                                                      (%)indoleto 1-ethyl-Selectivity                                                      (%)indole1-ethyl-Yield                       __________________________________________________________________________                                      of                                            1  0.5        A     39.5   71.0  28.0                                          2  1.0        B     59.9   67.9  40.7                                          3  2.0        C     58.7   71.9  42.2                                          4  3.0        D     53.3   83.5  44.5                                          __________________________________________________________________________

EXAMPLE 12

N-Ethylaniline and ethylene glycol were reacted at a contact time shown in Table 12 in the same manner as described in Example 1, whereby 1-ethylindole was obtained as a main product. The results are shown in the following Table 12.

    ______________________________________                                         Reaction conditions                                                            ______________________________________                                         Reaction temperature 300° C.                                            Initial partial pressure (atm)                                                 N--Ethylaniline vapor                                                                               0.0205                                                    Ethylene glycol vapor                                                                               0.0409                                                    Water vapor          0.778                                                     Nitrogen gas         0.161                                                     ______________________________________                                    

                  TABLE 12                                                         ______________________________________                                                            Conversion Selectivity                                                                            Yield of                                                    of N--ethyl-                                                                              to 1-ethyl-                                                                            1-ethyl-                                      Contact time (W/F)                                                                           aniline    indole  indole                                   No.  (g-cat · hr/mole)                                                                   (%)        (%)     (%)                                      ______________________________________                                         1    12.4          15.9       85.5    13.6                                     2    24.8          37.4       61.0    22.8                                     3    37.2          39.5       69.4    27.4                                     4    49.6          58.7       71.9    42.2                                     5    74.3          78.7       61.6    48.5                                     ______________________________________                                    

EXAMPLE 13

N-Ethylaniline and ethylene glycol were reacted in the same manner as described in Example 1 by adjusting the initial partial pressure as shown in Table 13, whereby 1-ethylindole was obtained as a main product. The results are shown in the following Table 13.

    ______________________________________                                         Reaction conditions                                                            ______________________________________                                         Reaction temperature 300° C.                                            Contact time (W/F)   49.6 g-cat · hr/mole                              ##STR9##             2                                                          Initial partial pressure (atm)                                               Nitrogen gas         0.161                                                     Water vapor    (A) 0.825 (B) 0.808                                                            (C) 0.778 (D) 0.716                                                            (E) 0.532                                                       ______________________________________                                    

                                      TABLE 13                                     __________________________________________________________________________        Initial partial                                                                               Conversion                                                                             Selectivity                                                                          Yield of                                          pressure of N--                                                                               of N--ethyl-                                                                           to 1-ethyl-                                                                          1-ethyl-                                          ethylaniline                                                                            Reaction                                                                             aniline indole                                                                               indole                                         No.                                                                               (atm)    conditions                                                                           (%)     (%)   (%)                                            __________________________________________________________________________     1  0.00462  A     70.3    45.9  32.3                                           2  0.0102   B     59.1    62.8  37.1                                           3  0.0205   C     58.7    71.9  42.2                                           4  0.0409   D     42.0    68.3  28.7                                           5  0.102    E     14.8    56.1  8.3                                            __________________________________________________________________________

EXAMPLE 14

N-Ethylaniline and ethylene glycol were reacted in the same manner as described in Example 1, by using benzene vapor as the diluent gas or without using said vapor, whereby 1-ethylindole was obtained as a main product. The results are shown in the following Table 14.

    ______________________________________                                         Reaction conditions                                                            ______________________________________                                         Contact time (W/F)   49.6 g-cat · hr/mole                             Initial partial pressure (atm)                                                 N--Ethylaniline vapor                                                                               0.0205                                                    Ethylene glycol vapor                                                                               0.0409                                                    Nitrogen gas         0.161                                                                      (A)    (B)                                                    Water vapor      0.778  0.659                                                  Benzene vapor    --     0.119                                                  ______________________________________                                    

                                      TABLE 14                                     __________________________________________________________________________                   Reaction                                                                              Conversion of                                                                          Selectivity to                                                                        Yield of                                      Benzene                                                                             Reaction                                                                             temperature                                                                           N--ethylaniline                                                                        1-ethylindole                                                                         1-ethylindole                              No.                                                                               vapor                                                                               conditions                                                                           (°C.)                                                                          (%)     (%)    (%)                                        __________________________________________________________________________     1  Nil  A     300    58.7    71.9   42.2                                                     350    57.9    6.6    3.8                                        2  Yes  B     300    37.3    87.1   32.5                                                     350    58.9    48.6   28.6                                       __________________________________________________________________________

EXAMPLE 15

N-Methylaniline and ethylene glycol were reacted at a contact time shown in Table 15 in the same manner as described in Example 1, whereby 1-methylindole was obtained as a main product. The results are shown in the following Table 15.

    ______________________________________                                         Reaction conditions                                                            ______________________________________                                         Reaction temperature     300° C.                                        Initial partial pressure (atm):                                                N--Methylaniline vapor   0.0205                                                Ethylene glycol vapor    0.0409                                                Water vapor              0.778                                                 Nitrogen gas             0.161                                                 ______________________________________                                    

                  TABLE 15                                                         ______________________________________                                                          Conversion  Selectivity                                                                             Yield of                                      Contact time                                                                               of N--methyl-                                                                              to 1-methyl-                                                                            1-methyl-                                     (W/F) (g-cat ·                                                                    aniline     indole   indole                                   No.  hr/mole)    (%)         (%)      (%)                                      ______________________________________                                         1    12.4        24.3        25.1      6.1                                     2    24.8        35.6        51.4     18.3                                     3    37.2        48.6        66.0     32.1                                     4    49.6        56.7        63.5     36.0                                     5    74.3        74.9        57.8     43.3                                     6    93.8        70.5        82.0     57.8                                     ______________________________________                                    

EXAMPLE 16

N-Benzylaniline and ethylene glycol were reacted at a molar ratio shown in Table 16 in the same manner as described in Example 1, whereby 1-benzylindole was obtained as a main product. The results are shown in the following Table 16.

    ______________________________________                                         Reaction condition                                                             ______________________________________                                         Reaction temperature 300° C.                                            Contact time (W/F)   49.6 g-cat · hr/mole                             Initial partial pressure (atm):                                                N--Benzylaniline vapor                                                                              0.0205                                                    Nitrogen gas         0.161                                                     Benzene vapor        0.119                                                     Water vapor     (A) 0.689                                                                               (B) 0.679                                                             (C) 0.659                                                                               (D) 0.638                                                             (E) 0.618                                                      ______________________________________                                    

                                      TABLE 16                                     __________________________________________________________________________      No.                                                                               ##STR10##   Reaction conditions                                                                 Conversion of Nbenzyl- aniline   (%)                                                    Selectivity to 1-benzyl- indole                                                     Yield of 1-benzyl- indole  (%)              __________________________________________________________________________     1  0.5           A     38.7   39.5  15.3                                       2  1.0           B     45.0   61.9  27.9                                       3  2.0           C     82.8   49.4  40.9                                       4  3.0           D     55.5   80.7  44.8                                       5  4.0           E     54.4   92.5  50.5                                       __________________________________________________________________________

EXAMPLE 17

Aniline and propylene glycol were reacted at a molar ratio shown in Table 17 in the same manner as described in Example 1, whereby 3-methylindole was obtained as a main product. The results are shown in the following Table 17.

    ______________________________________                                         Reaction conditions                                                            ______________________________________                                         Reaction temperature 300° C.                                            Contact time (W/F)   49.6 g-cat · hr/mole                             Initial partial pressure (atm):                                                Aniline vapor        0.0205                                                    Nitrogen gas         0.161                                                     Water vapor     (A) 0.808                                                                               (B) 0.798                                                             (C) 0.778                                                                               (D) 0.757                                                             (E) 0.737                                                      ______________________________________                                    

                                      TABLE 17                                     __________________________________________________________________________      No.                                                                               ##STR11##   Reaction conditions                                                                  Conversion of aniline   (%)                                                          Selectivity to 3-methyl- indole                                                       Yield of 3-methyl- indole                   __________________________________________________________________________                                       (%)                                          1  0.5           A    21.1   39.3   8.3                                        2  1.0           B    30.6   39.2  12.2                                        3  2.0           C    63.4   31.9  20.2                                        4  3.0           D    74.7   27.8  20.8                                        5  4.0           E    78.9   24.6  19.4                                        __________________________________________________________________________

EXAMPLE 18

N-Methylaniline and propylene glycol were reacted at a molar ratio shown in Table 18 in the same manner as described in Example 1, whereby 1,3-dimethylindole and 1,2-dimethylindole were obtained as main products. The results are shown in the following Table 18.

    ______________________________________                                         Reaction conditions                                                            ______________________________________                                         Reaction temperature 300° C.                                            Contact time (W/F)   49.6 g-cat · hr/mole                             Initial partial pressure (atm):                                                N--Methylaniline vapor                                                                              0.0205                                                    Nitrogen gas         0.161                                                     Water vapor     (A) 0.808                                                                               (B) 0.798                                                             (C) 0.778                                                                               (D) 0.757                                                             (E) 0.716                                                      ______________________________________                                    

                                      TABLE 18                                     __________________________________________________________________________      No.                                                                               ##STR12##   Reaction conditions                                                                  Main indoles produced                                                                   Conversion of Nmethyl- anilines                                                        Selectivity to main indoles                                                   produced (%)                                                                           Yield of main indoles                                                         produced (%)                      __________________________________________________________________________     1  0.5           A   1,3-dimethylindole                                                                        35.3    44.2   15.6                                                 1,2-dimethylindole 18.4    6.5                            2  1.0           B   1,3-dimethylindole                                                                        45.5    48.8   22.2                                                 1,2-dimethylindole 19.3    8.8                            3  2.0           C   1,3-dimethylindole                                                                        50.3    46.1   23.2                                                 1,2-dimethylindole 14.5    7.3                            4  3.0           D   1,3-dimethylindole                                                                        43.4    51.2   22.2                                                 1,2-dimethylindole 24.9   10.8                            5  5.0           E   1,3-dimethylindole                                                                        43.6    55.0   24.0                                                 1,2-dimethylindole 22.2    9.7                            __________________________________________________________________________

EXAMPLE 19

N-Methylaniline and propylene glycol were reacted at a contact time shown in Table 19 in the same manner as described in Example 1, whereby 1,3-dimethylindole and 1,2-dimethylindole were obtained as main products. The results are shown in the following Table 19.

    ______________________________________                                         Reaction conditions                                                            ______________________________________                                         Reaction temperature:    300° C.                                        Initial partial pressure (atm):                                                N--Methylaniline vapor   0.0205                                                Propylene glycol vapor   0.0409                                                Water vapor              0.778                                                 Nitrogen gas             0.161                                                 ______________________________________                                    

                                      TABLE 19                                     __________________________________________________________________________                           Conversion                                                                             Selectivity                                                                            Yield of                                                       of N--methyl-                                                                          to main indoles                                                                        main indoles                                Contact time (W/F)                                                                       Main indoles                                                                            aniline produced                                                                               produced                                 No.                                                                               (g-cat · hr/mole)                                                               produced (%)     (%)     (%)                                      __________________________________________________________________________     1  12.4      1,3-dimethylindole                                                                      18.0    26.7    4.8                                                   1,2-dimethylindole                                                                              15.6    2.8                                      2  24.8      1,3-dimethylindole                                                                      31.9    22.9    7.3                                                   1,2-dimethylindole                                                                              9.1     2.9                                      3  37.2      1,3-dimethylindole                                                                      47.9    38.2    18.3                                                  1,2-dimethylindole                                                                              15.4    7.4                                      4  46.9      1,3-dimethylindole                                                                      50.3    46.1    23.2                                                  1,2-dimethylindole                                                                              14.5    7.3                                      5  74.3      1,3-dimethylindole                                                                      58.0    49.8    28.9                                                  1,2-dimethylindole                                                                              14.3    8.3                                      6  93.8      1,3-dimethylindole                                                                      63.0    47.5    29.9                                                  1,2-dimethylindole                                                                              9.7     6.1                                      __________________________________________________________________________

EXAMPLE 20

N-Methylaniline and propylene oxide were reacted at a molar ratio shown in Table 20 in the same manner as described in Example 1, whereby 1,3-dimethylindole and 1,2-dimethylindole were obtained as main products. The results are shown in the following Table 20.

    ______________________________________                                         Reaction conditions                                                            ______________________________________                                         Reaction temperature 300° C.                                            Contact time (W/F)   49.6 g-cat · hr/mole                             Initial partial pressure (atm):                                                N--Methylaniline vapor                                                                              0.0205                                                    Nitrogen gas         0.161                                                     Water vapor     (A) 0.808                                                                               (B) 0.798                                                             (C) 0.778                                                                               (D) 0.757                                                             (E) 0.716                                                      ______________________________________                                    

                                      TABLE 20                                     __________________________________________________________________________      No.                                                                               ##STR13##   Reaction conditions                                                                  Main indoles produced                                                                   Conversion of Nmethyl- anilines                                                        Selectivity to main indoles                                                   produced (%)                                                                           Yield of main indoles                                                         produced (%)                      __________________________________________________________________________     1  0.5           A   1,3-dimethylindole                                                                        31.2    52.6   16.4                                                 1,2-dimethylindole 14.4    4.5                            2  1.0           B   1,3-dimethylindole                                                                        46.7    44.8   20.9                                                 1,2-dimethylindole 12.0    5.6                            3  2.0           C   1,3-dimethylindole                                                                        50.9    38.5   19.6                                                 1,2-dimethylindole  9.4    4.8                            4  3.0           D   1,3-dimethylindole                                                                        46.4    48.1   22.3                                                 1,2-dimethylindole 13.4    6.2                            5  5.0           E   1,3-dimethylindole                                                                        49.3    40.8   20.1                                                 1,2-dimethylindole 11.0    5.4                            __________________________________________________________________________ 

We claim:
 1. A process for preparing an indole which consists essentially of reacting in the vapor phase an aniline of the formula ##STR14## wherein R¹ is hydrogen, alkyl, aryl or aralkyl, R² is alkyl or alkoxy, and n is an integer of 0 to 4, with a glycol of the formula: ##STR15## wherein R³ and R⁴ are the same or different and stand for hydrogen or alkyl, and R⁵ and R⁶ are the same or different and stand for hydrogen or alkyl, or an oxide of the formula: ##STR16## wherein R³ and R⁴ are the same as defined above, at 250° to 400° C. in the presence of a solid acid catalyst selected from the group consisting of silica, alumina, and silica-alumina to give an indole of the formula: ##STR17## wherein R¹, R², R³, R⁴ and n are the same as defined above.
 2. The process according to claim 1, wherein the solid acid catalyst further contains a metal oxide selected from the group consisting of an alkali metal oxide, zinc oxide, chromium oxide, iron oxide and nickel oxide.
 3. The process according to claim 2, wherein the solid acid catalyst is silica-alumina catalyst containing a metal oxide selected from the group consisting of an alkali metal oxide, zinc oxide, chromium oxide, iron oxide and nickel oxide.
 4. The process according to claim 2, wherein the solid acid catalyst is silica-alumina catalyst containing an alkali metal oxide.
 5. The process according to claim 4, wherein the solid acid catalyst is silica-alumina catalyst containing sodium oxide.
 6. The process according to claim 1 or 2, wherein the vapor phase reaction is carried out by contacting a gaseous mixture of the aniline (I), the glycol (II) or the oxide (II'), and an inert diluent with the solid acid catalyst.
 7. The process according to claim 1 or 2, wherein the vapor phase reaction is carried out by contacting a gaseous mixture of the aniline (I), 0.5 to 10 moles of the glycol (II) or the oxide (II') per mole of said aniline (I), and an inert diluent with the solid acid catalyst at a contact time of 10 to 1,000 g-cat.hr/mole.
 8. The process according to claim 1 or 2, wherein the vapor phase reaction is carried out by contacting a gaseous mixture of the aniline (I), 0.5 to 10 moles of the glycol (II) or the oxide (II') per mole of said aniline (I), and an inert diluent with the solid acid catalyst at 275° to 350° C. at a contact time of 20 to 200 g-cat.hr/mole under atmospheric pressure. 